The present invention relates generally to packet-based networks, and more particularly, to a method and system for managing inhomogeneous self-similar traffic sources.
Call Admission Control (CAC) is a preventive method to avoid packet traffic congestion and to deliver required quality of services. In general, in the absence of an efficient CAC mechanism, packet dropping may increase without bounds, causing undesirable speech clipping or even call dropping. Undoubtedly, packet dropping probability is an important criterion in evaluating wireless/cellular packet communications. Packet access requests from ongoing calls are given priority over new call packet access by using a time out mechanism for new calls. New calls waiting more than a given amount of time are denied access to the resource and are cleared from the system. This scheme achieves graceful degradation in packet dropping for existing calls under heavy load conditions, while blocking most new calls. Packet dropping may increase drastically when more users become active. Efficient call admission control algorithms must be used to limit the packet dropping probability for ongoing calls to an adequately selected threshold while offering higher utilization of the scarce radio resource.
It is well known that Ethernet local area network (or “LAN”) traffic is statistically self-similar and is characterized by fractal-like behavior. As a result, such traffic exhibits scale-invariance which differs from traditional models of network traffic. It is also well-known that self-similarity degrades the network performance by requiring large queuing buffers, causing delay and packet dropping problems, as well as causing congestion problems. It is further known that the degree of self-similarity for an Ethernet LAN increases with higher loads. As a result, traditional queuing theory proved inadequate to predict performance. For example, ATM switch vendors once assumed that data traffic is a multiplex of a large number of independent traffic streams. Such an assumption resulted in a Poisson process and, as a result, the vendors produced switches with relatively small buffers on the order of 10-100 cells. However, in use, cell losses were beyond that expected and, as a result, the switches had to be redesigned.
It is also known that a traditional Poisson assumption can not adequately represent the state of art packet network environment. It is further known that the total capacity is not merely a summation of individual traffic sources. How to implement a realistic Call Admission Control (CAC) to admit n+1 traffic sources when there are n traffic sources existing is a common concern.
Various approaches have been done to search for an improved Call Admission Control mechanism based on a required capacity of the network. A CAC algorithm based on a required capacity for self-similar traffic was proposed by Wang and Erramilli in Globecom Conference in December 1999. The proposed algorithm is based on a “Scaling Law.” The major defect to this approach is that when a new source added, it is likely that the total required capacity is to be reduced. Referring to FIG. 1, two 2-dimensional plots are constructed having a number of sources as the X axis and a estimated required capacity as the Y axis. The plotted line labeled with “H1” represents the condition that the sources are nonhomogeneous, while “H2” is for the homogeneous sources. It is evident, that according to this approach, when the number of sources increases above 8, the required capacity actually drops. This is clearly wrong, and the unreliability of this approach remains to be improved. On the other hand, the algorithm attempts to handle homogeneous sources (i.e., all the involved sources have a same Hurst parameter). This restriction significantly limits the application of this algorithm since the existence of nonhomogeneous sources is a matter of fact.
What is needed is a reliable Call Admission Control mechanism based on required capacity that can reliably deal with nonhomogeneous self-similar traffic sources.